How to Select a Clutch or Brake

Clutch and/or Brake

At the most basic level, the designer will identify if the application calls for a clutch, a brake or a combination clutch and brake. A clutch would be used in applications where it is desirable to engage/disengage the load and motor while leaving the motor to run all of the time. When a clutch is used the load will be allowed to coast to a stop.

A brake would be used in applications where accurate stopping of the load is needed and the motor will stop as well. A clutch and brake combination would be used where the load will be started and stopped while the motor continues to rotate. For C-face mounted designs, all three choices are available. When making a unit selection there are several key steps that are common.

Mounting

C-Face Mounting

The next choice is unit mounting. Both clutches and clutch brakes can mount to the motor shaft or be base mounted and have input via a belt drive, chain drive or coupling.

Motor Horsepower and Frame Size

Base Mounting

Once function is determined, the next step is to define motor HP and motor frame size. In the case of base mounted units it may be necessary to define the RPM at that location. Manufacturers provide quick selection charts where unit size is determined by finding the intersection of Motor HP and Speed at the Clutch shaft. The charts are commonly created using the dynamic torque capacity for the product and the torque capacity for the motor plus an overload factor of some value. Using this method presumes that the designer has selected a motor that is sized appropriately to the application. In applications where cycle rates are considered aggressive for the inertia of the load, consulting with the application support staff of the manufacturer regarding heat dissipation capacity would be wise.

Horsepower vs. Shaft Speed

In some cases, a given motor HP may have more than one frame size choice. For instance, 1 HP motors can be either a 56C frame or a 143TC frame. Since this impacts shaft size, it is critical to know this. As with HP/RPM selection, manufacturers will provide charts such as the one below where unit size and frame size are shown. Since frame size determines unit shaft size, that factor would be pre-determined.

Frame Size Selection

Coil Voltage

The last remaining variable is coil voltage: 6, 24 and 90 volt DC are common options with 90 volt being widely preferred in North American markets, while 24 volt is more common in Europe. In both cases, clutch/brake manufacturers can provide power supplies to convert AC power to DC.